1. Field of the Invention
The present invention relates generally to gas turbine engines and, more particularly, to a modified structural frame in a turbine engine having axially curved polygonal panels.
2. Description of the Prior Art
Gas turbine engines typically include a core engine having a compressor for compressing air entering the core engine, a combustor where fuel is mixed with the compressed air and then burned to create a high energy gas stream, and a first or high pressure turbine which extracts energy from the gas stream to drive the compressor. In aircraft turbofan engines, a second turbine or low pressure turbine located downstream from the core engine extracts more energy from the gas stream for driving a forward fan. The forward fan provides the main propulsive thrust generated by the engine.
The static parts of a gas turbine engine, namely, frames, casings and mounts, are components that do not rotate but instead provide the overall backbone of the engine. These static components must maintain alignment between the rotors and stators of the engine. In many instances, this requirement dictates a need for stiffness, rather than strength, in the construction of the frames.
A structural frame component in a turbine engine typically is a static part that supports bearings which, in turn, support the rotatable rotors of the engine. The common elements of a structural frame component, such as a turbine rear structural frame located at the rear end of the low pressure turbine, are outer and inner shells and a plurality of circumferentially-spaced radial struts extending between the shells.
Heretofore, the panels forming the outer shell configuration have low critical buckling stress resistance and thus require circumferential stiffening ribs to increase buckling resistance capability under compression loads. However, the stiffening ribs provide sites for concentration of stresses and initiation of cracks.
Consequently, a need exists for an alterative design for a rear structural frame that will increase buckling resistance without introducing any new problems.